This invention is concerned with the improvement of plastic retractable pouring spout closures commonly empolyed in dispensing liquid products from metal or plastic containers. One such pouring spout closure in wide usage consists of a plastic nozzle with integrally connected captive cap and having a tear out sealing diaphragm closing off the uppermost end of the nozzle throat. An elongated pouring spout is held by its upper end in retracted or stored position within the nozzle throat and is lifted to raised pouring position and rigidly seated within the nozzle upon removal of the sealing diaphragm.
The specific problem to which the invention is directed has to do with the common occurrence of pressure buildup within the container as a result of an almost unavoidable temperature differential existing between filling and initial dispensing of the container. In certain instances this temperature differential is such as to result in a relatively harmless, negative pressure. In many other instances, however, the filling operation is carried out at a much lower temperature than the ambient end use conditions, resulting frequently in a rather sudden release of internal pressure upon opening the container. Unless this internal pressure is dissipated in a safe and controlled manner, a substantial hazard is created due to the tendency of the liquid to gush or squirt out of the container upon opening. This gushing results from a pressure buildup in the container which, upon removal of the sealing diaphragm, forces the liquid up through the partially submerged spout. The problem thus becomes one of providing some means for assuring that the pressure within the container is safely vented to the atmosphere prior to dispensing.
Various approaches to a solution have presented themselves heretofore without complete success. One such approach is to provide a separate vent fitting in the container so that the internal pressure can be relieved prior to dispensing. This approach suffers from reliance on the human element. If the vent is not opened first, a hazard exists. Another approach is to provide a separate plug to close off the upper end of the spout, allowing the pressure to vent harmlessly through the nozzle about the spout exterior. The additional molding and assembly operations involved with this arrangement introduce a substantial cost factor weighing heavily against marketability. Going a step further, it has been proposed to mold an integral sealing diaphragm closing off the upper end of the pouring spout for removal after venting. This arrangement, however, poses somewhat of a molding problem and in certain instances seriously limits the spout design.